1. Field of the Invention
This invention relates to binders based on homopolymers or copolymers of styrene, to their production and to their use for bonding, coating and sealing.
Binders in the context of the invention are substances which are capable of bonding or firmly adhering to substrates of the same or different types. They are generally based on substances, especially polymers, which set chemically or physically. Physical setting consists in solidification from the melt or in the drying of an aqueous or organic solution or dispersion. The substances or rather polymers are generally modified by additives in such a way that they are more suitable for bonding, adhesive sealing and coating. Corresponding additives are, for example, resins, plasticizers, solvents, fillers, pigments, accelerators, stabilizers and dispersants. Accordingly, the adhesives, sealing compounds and coating compounds are based on correspondingly modified binders.
2. Discussion of Related Art
Plasticizers are added to improve the plasticity or to reduce the hardness of adhesives, sealing compounds and coating compositions. Plasticizers are liquid or solid, generally inert organic substances of low vapor pressure. According to general expert knowledge (see Habenicht, Gerd: xe2x80x9cKleben: Grundlagen, Technologie-Anwendungenxe2x80x9d, 2nd Edition,1990, page 100), the disadvantage of plasticizer-containing adhesive layers lies in their impaired ageing and adhesion properties and in the reduced strengths of the adhesive layer and in its tendency to creep and migrate. Accordingly, well-balanced consideration has to be given to the priorities between plasticity on the one hand and strength of the other hand. In xe2x80x9cUllmanns Encyclopxc3xa4die der technischen Chemiexe2x80x9d, the use of plasticizers is also described under the keyword xe2x80x9cWeichmacher (Plasticizer)xe2x80x9d (see pages 371 to 377, Vol. 24, 4th Edition, 1983).
Corresponding compositions of polystyrene and plasticizers are known. Thus, U.S. Pat. No. 4,869,934 describes a composition for the smoothing, cleaning and coating of floors which consists, for example, of the following components: 31.2 parts by weight of a copolymer of butyl methacrylate, methacrylic acid, methyl methacrylate and styrene in a ratio of 10:18:52:20, 1.6 parts by weight of the permanent plasticizer (BuOCH2CH2O)3PO and 7.0 parts by weight of the volatile plasticizer Me(OC3H6)2OH and around 48 parts by weight of water. This known composition has the disadvantage that the volatile plasticizers at least pollute the environment or are even toxic.
The product xe2x80x9cPlastilit 3060xe2x80x9d is described in BASF""s Technical Information Pamphlet TI/ED 1115 d-1 of January 1984. This product is a polypropylene glycol alkylphenyl ether which is used as a plasticizer for polymer dispersions, more especially for polyacrylates. The polymers specifically mentioned include a copolymer of styrene and butyl acrylate and a copolymer of ethyl acrylate, ethyl hexyl acrylate and acrylonitrile. Corresponding compositions may be used, for example, as sealing compounds with rapid skin formation after application, with relatively little post-curing and with better elongation behavior at low temperatures. In addition, they form with fillers paste-like tile adhesives which combine high tensile strengths with high elasticity. The plasticizer has an elasticizing effect on the copolymer without significantly impairing the water absorption of the film. Thus, the elongation of a film increases substantially linearly from around 300% to 4,000% where 9% of plasticizer is added. So far as the biological activity of the plasticizer is concerned, it is said not to be a health risk although prolonged exposure may well result in irritation of the skin and mucous membrane.
The same disadvantages also apply to the following two publications. Polish patent PL 119091 describes a non-toxic and non-inflammable adhesive for ceramics and plastics which, in addition to an acrylate/styrene dispersion, contains polypropylene glycol alkylphenyl ether, fillers, organic solvents and water.
German patent DE 36 38 224 describes an elastic sealing material which contains a styrene/butadiene rubber, an xcex1-methyl styrene polymer, solvents, such as hydrocarbons and aromatic hydrocarbons, and polypropylene glycol alkylphenyl ether.
Czechoslovakian patent CS 259825 describes a contact adhesive for labels and tapes which mainly contains a copolymer of acrylates, unsaturated carboxylic acids and, optionally, styrene, alkyl styrene or vinyl acetate. Other components are organic solvents, plasticizers such as, for example, polyethylene glycol and polypropylene glycol.
Against the background of this prior art, the problem addressed by the present invention was to provide a toxicologically safe composition of a styrene polymer and a plasticizer free from aromatic constituents which would be suitable for use as a binder and which would provide acceptable adhesion.
The solution provided by the invention is defined in the claims and is characterized in that the styrene polymer contains a relatively large quantity of styrene while the plasticizer is a fatty compound.
The styrene polymer contains styrene or methyl styrene in a quantity of, preferably, more than 30% by weight, in particular more than 50% by weight and, above all, more than 80% by weight of the monomers. Comonomers of styrene or methyl styrene can be acrylates and methacrylates containing 1 to 12 carbon atoms in the alcohol component and, more particularly, 2 to 8 carbon atoms. The acrylates may also contain reactive groups for subsequent crosslinking. Corresponding reactive groups may also contain vinyl comonomers, for example a silane group. The Si(Alk)3 group may be attached to the vinyl group either directly or by a (CH2)n radical where n may be a number of 2 to 6 and preferably has a value of 3 or 0. The alkyl groups may contain 1 to 4 carbon atoms and preferably 1 or 2 carbon atoms. Other comonomers can be vinyl esters, maleic acid esters (again containing 1 to 12 and preferably 2 to 8 carbon atoms in the alcohol component), ethylene, acrylamide, acrylic acid, butadiene, acrylonitrile both individually and in the form of mixtures. The molecular weight is above 100,000 g/mole. Commercially available styrene copolymers are: Acronal 290 D, Scopacryl D 343, Ubatol VAF 1539, Acronal S 360 D, Scopacryl PAA D 8875, Acronal S 400, Acronal S 401, Styrofan A 900, Rhodopas DS 913, Joncryl 678, Vinnapas LL 6010 and SAF 54, Neocryl A 621 (styrene/acrylate copolymer), Pliotec LS 1 (styrene/butyl acrylate/methacrylic acid terpolymer), Mowilith DM 611, Mowilith DM 680, Styropor P 555 (pure styrene), Buna EM 2116, Styrolux 684 D, Rhodopas SB 012, (styrene/butadiene copolymer), Novodur P2M, Synthomer VL 10286 (styrene/butadiene/acrylonitrile terpolymer).
The styrene copolymers may be produced by known methods, more particularly by emulsion or bead polymerization. These processes give aqueous dispersions with a concentration of around 40 to 70% by weight of styrene copolymer. However, the styrene copolymers may also be produced in bulk or solution.
It may be regarded as surprising that these aromatic polymers are compatible with the aliphatic fatty compounds. It may also be regarded as surprisingxe2x80x94in view of the constant need to dry and degrease the substrate surfaces to ensure firm adhesionxe2x80x94that strength is hardly affected in the process. This is particularly surprising insofar as the content of fatty compounds is not just a few percent, but generally from 0.5 to 60% by weight, preferably from 10 to 50% by weight and, more preferably, from 15 to 40% by weight, based on the binder. The tensile shear strength of adhesives is still  greater than 1, preferably  greater than 2 and, more preferably,  greater than 4 N/mm2 for beechwood.
xe2x80x9cFatty compoundsxe2x80x9d in the context of the invention are fatty acids, fatty alcohols and derivatives thereof. Their molecular weight is generally above 100 and preferably above 200. The upper limit is 20,000 and preferably 300 to 1,500.
xe2x80x9cFatty acidsxe2x80x9d in the context of the invention are acids which contain one or more carboxyl groups (xe2x80x94COOH). The carboxyl groups may be attached to saturated, unsaturated, unbranched or branched alkyl radicals containing more than 8 carbon atoms and, in particular, more than 12 carbon atoms. In addition to the xe2x80x94OH, xe2x80x94SH, xe2x80x94Cxe2x95x90Cxe2x80x94, xe2x80x94COOH, amino, anhydride groups or epoxide groups described above, they may contain other groups, such as ether, ester, halogen, amide, amino, urethane and urea groups. However, carboxylic acids, such as native fatty acids or fatty acid mixtures, dimer fatty acids and trimer fatty acids are preferred. Specific examples of the fatty acids apart from the saturated types are, in particular, the monounsaturated or polyunsaturated acids palmitoleic, oleic, elaidic, petroselic, erucic, ricinoleic, hydroxymethoxystearic, 12-hydroxystearic, linoleic, linolenic and gadoleic acid.
Products emanating from the Guerbet condensation of linear saturated or unsaturated fatty alcohols with subsequent oxidation may also be used as fatty acids. Examples include 2-ethyl hexanoic acid, 2-butyl octanoic acid, 2-hexyl decanoic acid, 2-decyl tetradecanoic acid, 2-tetradecyl octadecanoic acid, 2-hexadecyl-C20-acid or mixtures thereof. In addition, isostearic acid as a secondary product of the dimerization of fatty acids is also suitable.
In addition to the naturally occurring fatty acids, polyhydroxyfatty acids may also be used. They may be obtained, for example, by epoxidation of unsaturated fats and oils or esters of fatty acids with alcohols, ring opening with H-active compounds, for example alcohols, amines and carboxylic acids, and subsequent saponification. The fats or oils required as starting material may be both of vegetable origin and of animal origin or may optionally be obtained by particular petrochemical syntheses.
The fatty acids may also be derived from oil- and fat-based raw materials obtainable, for example, by ene reactions, Diels-Alder reactions, transesterifications, condensation reactions, grafting (for example with maleic anhydride or acrylic acid, etc.) and epoxidations. Examples of corresponding raw materials are: a) epoxides of unsaturated fatty acids, such as palmitoleic acid, oleic acid, elaidic acid, petroselic acid, erucic acid, linoleic acid, linolenic acid, gadoleic acid; b) reaction products of unsaturated fatty acids with maleic acid, maleic anhydride, methacrylic acid or acrylic acid; c) condensation products of hydroxycarboxylic acids, such as ricinoleic acid or 12-hydroxystearic acid, and polyhydroxycarboxylic acids.
Not all the fatty acids described above are stable at room temperature. If necessary, therefore, derivatives of the above-mentioned fatty acids, such as esters or amides, may be used for the purposes of the invention.
One preferred embodiment of the invention is characterized by the use of esters or partial esters of the above-mentioned fatty acids with monohydric or polyhydric alcohols. xe2x80x9cAlcoholsxe2x80x9d in the present context are understood to be hydroxyl derivatives of aliphatic and alicyclic saturated, unsaturated, unbranched or branched hydrocarbons. Besides monohydric alcohols, this definition also encompasses the low molecular weight hydroxyfunctional chain extending or crosslinking agents known per se from polyurethane chemistry. Specific examples of low molecular weight types are methanol, ethanol, propanol, butanol, pentanol, decanol, octadecanol, 2-ethyl hexanol, 2octanol, ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, 2,3-butylene glycol, hexamethylenediol, octamethylenediol, neopentyl glycol, 1,4-bis-hydroxymethyl cyclohexane, Guerbet alcohol, 2-methyl propane-1,3-diol, hexane-1,2,6-triol, glycerol, trimethylol propane, trimethylol ethane, pentaerythritol, sorbitol, formitol, methyl glycoside, butylene glycol, the dimer and trimer fatty acids reduced to alcohols. Alcohols derived from pine resins, such as abietyl alcohol, may also be used for the esterification reaction.
Instead of alcohols, it is also possible to use OH-containing tertiary amines, polyglycerol or partly hydrolyzed polyvinyl esters.
In addition, polycarboxylic acids or hydroxycarboxylic acids may be added for the oligomerization reaction. Examples of such acids are oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, suberic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid or dimer fatty acid, trimer fatty acid, citric acid, lactic acid, tartaric acid, ricinoleic acid, 12-hydroxystearic acid. Adipic acid is preferably used.
Examples of suitable esters besides the partly saponified fats, such as glycerol monostearate, are preferably the natural fats and oils of rape (new and old), sunflowers, soya, linseed, castor, coconuts, oil palms, oil palm kernels and oil trees and methyl esters thereof. Preferred fats and oils are, for example, beef tallow with a chain distribution of 67% oleic acid, 2% stearic acid, 1% hetpadecanoic acid, 10% saturated C12 to C16 acids, 12% linoleic acid and 2% saturated acids containing more than 18 carbon atoms or, for example, the oil of new sunflowers (NSf) with a composition of around 80% oleic acid, 5% stearic acid, 8% linoleic acid and around 7% palmitic acid. The corresponding epoxides and reaction products with maleic anhydride, for example, may of course also be used. Other examples are partly and completely dehydrated castor oil, partly acetylated castor oil, ring opening products of epoxidized soybean oil with dimer fatty acid.
In addition, fatty acid esters and derivatives thereof obtainable by epoxidation may also be used. Examples of such esters are soybean oil fatty acid methyl ester, linseed oil fatty acid methyl ester, ricinoleic acid methyl ester, epoxystearic acid methyl ester, epoxystearic acid-2-ethylhexyl ester. Preferred glycerides are triglycerides, for example rapeseed oil, linseed oil, soybean oil, castor oil, partly and completely dehydrated castor oils, partly acetylated castor oil, soybean oil epoxide, linseed oil epoxide, rapeseed oil epoxide, epoxidized sunflower oil.
Epoxidized triglycerides of unsaturated fatty acids ring-opened with nucleophiles are preferably used. Nucleophiles are understood to be alcohols such as, for example, methanol, ethanol, ethylene glycol, glycerol or trimethylol propane, amines such as, for example, ethanolamine, diethanolamine, triethanolamine, ethylenediamine or hexamethylenediamine or carboxylic acids such as, for example, acetic acid, dimer fatty acid, maleic acid, phthalic acid or a mixture of C6-36 fatty acids.
The fats and oils (triglycerides) may be used both in native form and after thermal and/or oxidative treatment or in the form of the derivatives obtainable by epoxidation or by the addition of maleic anhydride or acrylic acid. Specific examples are palm oil, peanut oil, rapeseed oil, cottonseed oil, soybean oil, castor oil, partly and completely dehydrated castor oils, partly acetylated castor oils, sunflower oil, linseed oil, stand oils, blown oils, epoxidized soybean oil, epoxidized linseed oil, rapeseed oil, coconut oil, palm kernel oil and tallows.
Other suitable derivatives of the above-mentioned fatty acids are the amides which may be obtained by reaction with primary and secondary amines or polyamines, for example with monoethanolamine, diethanolamine, ethylenediamine, hexamethylenediamine, ammonia.
xe2x80x9cFatty alcoholsxe2x80x9d in the context of the invention are understood to be compounds which contain one or more hydroxyl groups. The hydroxyl groups may be attached to saturated, unsaturated, unbranched or branched alkyl radicals containing more than 8 carbon atoms and, in particular, more than 12 carbon atoms. In addition to the xe2x80x94SH, xe2x80x94Cxe2x95x90Cxe2x80x94, xe2x80x94COOH, amino, anhydride groups or epoxide groups required for subsequent reaction with the alkylene oxides, they may contain other groups, for example ether, ester, halogen, amide, amino, urea and urethane groups. Specific examples of the fatty alcohols according to the invention are ricinoleyl alcohol, 12-hydroxystearyl alcohol, oleyl alcohol, erucyl alcohol, linoleyl alcohol, linolenyl alcohol, arachidyl alcohol, gadoleyl alcohol, erucyl alcohol, brassidyl alcohol, dimerdiol (=hydrogenation product of dimer fatty acid methyl ester).
Branched alcohols, so-called Guerbet alcohols, emanating from the condensation of linear, saturated or unsaturated alcohols may also be used. Examples of Guerbet alcohols are 2-ethyl hexanol, 2-butyl octanol, 2-hexyl decanol, 2-tetradecyl octadecanol, 2-hexadecyl-C20-alcohol, also isostearyl alcohol and mixtures resulting from the guerbetization of technical alcohols.
Symmetrical and asymmetrical ethers and esters with mono- and polycarboxylic acids may be used as derivatives of the fatty alcohols. Monocarboxylic acids are understood to be formic, acetic, propionic, butyric, valeric, caproic, oenanthic, caprylic, pelargonic, capric, undecanoic, lauric, tridecanoic, myristic, pentadecanoic, palmitic, margaric, stearic, nonadecanoic, arachic, behenic, lignoceric, cerotic and melissic acid. Polycarboxylic acids are, for example, oxalic acid, adipic acid, maleic acid, tartaric acid and citric acid. At the same time, the fatty acids described above, for example oleic acid oleyl ester, may be used as the carboxylic acid.
The fatty alcohols may also be etherified, more especially with polyhydric alcohols, for example alkyl polyglycosides, dimer diol ethers.
The ratio by weight of the styrene polymer to the plasticizing fatty compound is 100:0.5 to 50, preferably 100:2.5 to 40 and, above all, 100:7.5 to 15.
Besides these two key components, the binders according to the invention may contain other ingredients, for example antioxidants, pigments, fillers, plasticizers, preservatives, defoamers, film-forming agents, fragrances, water, adhesion promoters, solvents, dyes, flameproofing agents, flow controllers, resins, tackifiers, viscosity regulators, dispersion aids (for example sodium or ammonium salt of polyacrylic acid), emulsifiers (for example alkyl ether phosphates and sulfosuccinates) and thickeners (for example MC, HEG).
Suitable resins are polyisobutylene or polybutylene (for example Hyvis 10, a product of BP), pine resins and derivatives (esters, hydrogenated products, abietyl alcohol), acrylate resins, phenolic resins, terpene/phenol resins, polyterpenes, epoxy resins, hydrocarbon resins, indene/coumarone resins and melamine resins.
Examples of suitable antioxidants are phosphorous acid and salts thereof, hypophosphorous acid and salts thereof, ascorbic acid and derivatives thereof (especially ascorbyl palmitate), tocopherol and derivatives thereof, mixtures of ascorbic acid derivatives and tocopherol derivatives, sterically hindered phenol derivatives, especially BHA (tert.butyl4-methoxyphenol) and BHT (2,6ditert.butyl4-methylphenol), gallic acid and derivatives thereof, especially alkyl gallates, aromatic amines, for example diphenylamine, naphthylamine and 1,4-phenylenediamine, dihydroquinoline, organic sulfides and polysulfides, dithiocarbamates and mercaptobenzimidazole.
Examples of viscosity regulators are cellulose ethers, hydrogenated castor oil, highly dispersed silicas and ionic and nonionic thickeners such as, for example, polyacrylic acid and associated thickeners.
Suitable fillers and pigments are chalk, heavy spar, kaolin, carbon black, gypsum, aerosil, silica gel, kaolins, talcum, graphite, metal oxides of aluminium, iron, zinc, titanium, chromium, cobalt, nickel, manganese, etc., optionally as mixed oxides, chromates, molybdates, carbonates, silicates, aluminates, sulfates, native fibers, cellulose, wood chips, phthalocyanines and silica flour.
In a preferred embodiment, the fatty compounds are used as sole plasticizers. In particular, no polyalkylene oxides or oleochemical derivatives thereof are used as plasticizers.
The binder according to the invention is generally prepared from the starting materials as follows:
The plasticizer according to the invention may be added to the polymer or to the polymer dispersion after, during or before the polymerization reaction. The formulations are generally produced by initially introducing the polymer or the polymer dispersion and then adding the other components with stirring (optionally at elevated temperature).
The binder may be liquid, paste-like or solid at room temperature (20xc2x0 C.). In one particular embodiment, it is liquid and best assumes the form of an aqueous dispersion with a solids content of 20 to 85% by weight, preferably 35 to 80% by weight and more preferably 45 to 75% by weight.
The solids content for emulsions or suspensions of the binder according to the invention is between 20 and 75% by weight and preferably between 40 and 60% by weight.
The plasticizers according to the invention can generally bring about the following changes to the styrene polymer:
The glass transition temperature is reduced.
The copolymer is tackified.
The viscosity is partly increased and partly reduced.
Breaking elongation is drastically increased.
Elongation under maximal force is also greatly increased which is indicative of rubber-elastic behavior.
However, it is of particular importance that these effects are permanent, i.e. no migration of the plasticizer was observed after 3 weeks at 60xc2x0 C. This is confirmed by the following test: the films were stored between sheets of silicone paper for 3 weeks at 60xc2x0 C. and were evaluated for staining of the paper at intervals of 3 days.
By virtue of these properties, the compositions according to the invention are suitable as binders for the production of adhesives, sealing compounds and coating compositions.
Specific examples of adhesives are hotmelt adhesives, solvent-based adhesives, dispersion adhesives, assembly adhesives, pressure-sensitive and contact adhesives and also redispersion powders, multipurpose adhesives and adhesive sticks. Materials which may be bonded with these adhesives include paper, paperboard, wood, textiles, wall coverings, tiles, labels, leather, rubber, plastics, glass, ceramic and metal. Examples of coatings include plastisols, dispersion paints and the insulation of roofs. The sealing compounds may be used both in the building industry and in the automotive industry. The composition according to the invention may also be added to hydraulic binders, for example cement or gypsum, to elasticize them or improve their adhesion.
The invention is illustrated by the following Examples: